1. Field of the Invention
The present invention relates to a resist composition for use in a process for producing a semiconductor such as an IC, a process for producing a circuit board for e.g., a thermal head or a liquid crystal, and other photofabrication processes, and relates to a method of forming a pattern by use of the composition. More particularly, the present invention relates to a resist composition that finds appropriate application when an exposure light source emits far-ultraviolet rays, electron beams or the like of wavelength 250 nm or shorter, preferably 220 nm or shorter, and also relates to a method of forming a pattern by use of the composition.
2. Description of the Related Art
A chemical amplification photosensitive composition is a pattern forming material that is capable of, upon exposure to far-ultraviolet or other radiation, generating an acid at the exposed area and, by a reaction catalyzed by the acid, changing the solubility in a developer between the area having been exposed to actinic radiation and the nonexposed area to thereby attain pattern formation on a substrate.
In using a KrF excimer laser as an exposure light source, a resin whose fundamental skeleton consists of a poly(hydroxystyrene) exhibiting a low absorption mainly in the region of 248 nm is employed as a major component of the composition. Accordingly, there can be attained a high sensitivity, high resolving power and favorable pattern formation. Thus, a system superior to the conventional naphthoquinone diazide/novolak resin system is realized.
In contrast, in using a light source of a further shorter wavelength, for example, an ArF excimer laser (193 nm), as an exposure light source, as the compounds having an aromatic group inherently exhibit a sharp absorption in the region of 193 nm, the above-mentioned chemical amplification system has not been satisfactory.
Therefore, resists for an ArF excimer laser containing a resin with an alicyclic hydrocarbon structure have been developed. For example, patent references 1 and 2 below describe compositions containing resins each simultaneously having a polycyclic acid-decomposable repeating unit and a non-acid-decomposable repeating unit. These resins without exception provide a chemical amplification resist having a protective group that is dissociated by an acid, thus being unstable to acids. However, in the current situation in which a further nanonization of resist pattern is demanded, it has become difficult to obtain a satisfactory resist performance by the employment of these resins only. Accordingly, a technology involving blending multiple polymers with each other has been proposed. For example, patent references 3 to 5 below describe the development of a technology involving blending of a polymer containing a fluorine atom.
However, the conventional resist compositions have been unsatisfactory in some respects, and further improvement has been demanded on the LWR, exposure latitude and pattern collapse performance.
[Patent reference 1] Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 2003-167347,
[Patent reference 2] JP-A-2003-223001,
[Patent reference 3] JP-A-2007-249192,
[Patent reference 4] JP-A-2008-102276, and
[Patent reference 5] JP-A-2008-88343.